88 BIG SPRING PRAIRIE. 
clusively that this area was a lake in past glacial times, 
and incidentally corroborates the conclusion that it was 
a preglacial drainage valley, as the rock strata near the 
western end of prairie are 30 feet beneath the surface. 
As the surface level is lower here than at the points 
before mentioned, it is evident that the stream flowed 
northward and westward. The gravel, sand and marl 
were deposited when the lake was quite deep, and be- 
fore the abundant aquatic plant life became established. 
The position of the clay bed seems to confirm Lesque- 
reaux’s explanation in regard to formation of such strata 
in ponds and sluggish streams from the remains of 
chara and allied plants. After bulrushes and cat-tails 
made their appearance the formation of the muck 
layer began, Aftera shallow layer of muck had accu- 
mulated over the clay bed, the area must have become 
sufficiently elevated to secure natural drainage enough 
to enable tree seedlings to make their appearance. 
The clay subsoil offered a sufficiently firm support 
for successful tree growth. After the forest became 
established, it is possible that the natural drainage 
outlet became obstructed, perhaps by the beaver dam 
before mentioned. In consequence the forest would 
be flooded and the trees destroyed. 
Buried forests have also been reported as occur- 
ing on the Vanlue end of the prairie, and may in the 
future be found to have existed on other unexplored 
portions. It is indeed a peculiar area scientifically, as 
it is proving practically to the celery and onion grow- 
ers. 
THE PRAIRE UNDER CULTIVATION. 
Before the first artificial drainage, the cultivation 
of any portion of the prairie was impossible. Even 
after the first artificial drainage, only isolated portions 
were cultivated Drainage was resorted to chiefly to 
render the prairie safer for pasturage, as cattle and 
horses frequently mired in this marsh. 
